Encode consists of a collection of modules whose details are too extensive to fit in one document. This one itself explains the top-level APIs and general topics at a glance. For other topics and more details, see the documentation for these modules:

The Encode module provides the interface between Perl strings and the rest of the system. Perl strings are sequences of characters.

The repertoire of characters that Perl can represent is a superset of those defined by the Unicode Consortium. On most platforms the ordinal values of a character as returned by ord(S) is the Unicode codepoint for that character. The exceptions are platforms where the legacy encoding is some variant of EBCDIC rather than a superset of ASCII; see perlebcdic.

During recent history, data is moved around a computer in 8-bit chunks, often called "bytes" but also known as "octets" in standards documents. Perl is widely used to manipulate data of many types: not only strings of characters representing human or computer languages, but also "binary" data, being the machine's representation of numbers, pixels in an image, or just about anything.

When Perl is processing "binary data", the programmer wants Perl to process "sequences of bytes". This is not a problem for Perl: because a byte has 256 possible values, it easily fits in Perl's much larger "logical character".

8 bits of data, with ordinal values 0..255; term for bytes passed to or from a non-Perl context, such as a disk file, standard I/O stream, database, command-line argument, environment variable, socket etc.

Encodes the scalar value STRING from Perl's internal form into ENCODING and returns a sequence of octets. ENCODING can be either a canonical name or an alias. For encoding names and aliases, see "Defining Aliases". For CHECK, see "Handling Malformed Data".

CAVEAT: the input scalar STRING might be modified in-place depending on what is set in CHECK. See "LEAVE_SRC" if you want your inputs to be left unchanged.

For example, to convert a string from Perl's internal format into ISO-8859-1, also known as Latin1:

$octets = encode("iso-8859-1", $string);

CAVEAT: When you run $octets = encode("utf8", $string), then $octets might not be equal to $string. Though both contain the same data, the UTF8 flag for $octets is always off. When you encode anything, the UTF8 flag on the result is always off, even when it contains a completely valid utf8 string. See "The UTF8 flag" below.

This function returns the string that results from decoding the scalar value OCTETS, assumed to be a sequence of octets in ENCODING, into Perl's internal form. As with encode(), ENCODING can be either a canonical name or an alias. For encoding names and aliases, see "Defining Aliases"; for CHECK, see "Handling Malformed Data".

CAVEAT: the input scalar OCTETS might be modified in-place depending on what is set in CHECK. See "LEAVE_SRC" if you want your inputs to be left unchanged.

For example, to convert ISO-8859-1 data into a string in Perl's internal format:

$string = decode("iso-8859-1", $octets);

CAVEAT: When you run $string = decode("utf8", $octets), then $string might not be equal to $octets. Though both contain the same data, the UTF8 flag for $string is on. See "The UTF8 flag" below.

Returns the encoding object corresponding to MIME_ENCODING. Acts same as find_encoding() but mime_name() of returned object must match to MIME_ENCODING. So as opposite of find_encoding() canonical names and aliases are not used when searching for object.

Converts in-place data between two encodings. The data in $octets must be encoded as octets and not as characters in Perl's internal format. For example, to convert ISO-8859-1 data into Microsoft's CP1250 encoding:

from_to($octets, "iso-8859-1", "cp1250");

and to convert it back:

from_to($octets, "cp1250", "iso-8859-1");

Because the conversion happens in place, the data to be converted cannot be a string constant: it must be a scalar variable.

from_to() returns the length of the converted string in octets on success, and undef on error.

Equivalent to $octets = encode("utf8", $string). The characters in $string are encoded in Perl's internal format, and the result is returned as a sequence of octets. Because all possible characters in Perl have a (loose, not strict) UTF-8 representation, this function cannot fail.

Equivalent to $string = decode("utf8", $octets [, CHECK]). The sequence of octets represented by $octets is decoded from UTF-8 into a sequence of logical characters. Because not all sequences of octets are valid UTF-8, it is quite possible for this function to fail. For CHECK, see "Handling Malformed Data".

CAVEAT: the input $octets might be modified in-place depending on what is set in CHECK. See "LEAVE_SRC" if you want your inputs to be left unchanged.

The canonical name of a given encoding does not necessarily agree with IANA Character Set Registry, commonly seen as Content-Type: text/plain; charset=WHATEVER. For most cases, the canonical name works, but sometimes it does not, most notably with "utf-8-strict".

As of Encode version 2.21, a new method mime_name() is therefore added.

If CHECK is 0, encoding and decoding replace any malformed character with a substitution character. When you encode, SUBCHAR is used. When you decode, the Unicode REPLACEMENT CHARACTER, code point U+FFFD, is used. If the data is supposed to be UTF-8, an optional lexical warning of warning category "utf8" is given.

If CHECK is set to Encode::FB_QUIET, encoding and decoding immediately return the portion of the data that has been processed so far when an error occurs. The data argument is overwritten with everything after that point; that is, the unprocessed portion of the data. This is handy when you have to call decode repeatedly in the case where your source data may contain partial multi-byte character sequences, (that is, you are reading with a fixed-width buffer). Here's some sample code to do exactly that:

For encodings that are implemented by the Encode::XS module, CHECK==Encode::FB_PERLQQ puts encode and decode into perlqq fallback mode.

When you decode, \xHH is inserted for a malformed character, where HH is the hex representation of the octet that could not be decoded to utf8. When you encode, \x{HHHH} will be inserted, where HHHH is the Unicode code point (in any number of hex digits) of the character that cannot be found in the character repertoire of the encoding.

The HTML/XML character reference modes are about the same. In place of \x{HHHH}, HTML uses &#NNN; where NNN is a decimal number, and XML uses &#xHHHH; where HHHH is the hexadecimal number.

These modes are all actually set via a bitmask. Here is how the FB_XXX constants are laid out. You can import the FB_XXX constants via use Encode qw(:fallbacks), and you can import the generic bitmask constants via use Encode qw(:fallback_all).

If the Encode::LEAVE_SRC bit is not set but CHECK is set, then the source string to encode() or decode() will be overwritten in place. If you're not interested in this, then bitwise-OR it with the bitmask.

As of Encode 2.12, CHECK can also be a code reference which takes the ordinal value of the unmapped character as an argument and returns octets that represent the fallback character. For instance:

$ascii = encode("ascii", $utf8, sub{ sprintf "<U+%04X>", shift });

Acts like FB_PERLQQ but U+XXXX is used instead of \x{XXXX}.

Even the fallback for decode must return octets, which are then decoded with the character encoding that decode accepts. So for example if you wish to decode octets as UTF-8, and use ISO-8859-15 as a fallback for bytes that are not valid UTF-8, you could write

CANONICAL_NAME will be associated with $object. The object should provide the interface described in Encode::Encoding. If more than two arguments are provided, additional arguments are considered aliases for $object.

Before the introduction of Unicode support in Perl, The eq operator just compared the strings represented by two scalars. Beginning with Perl 5.8, eq compares two strings with simultaneous consideration of the UTF8 flag. To explain why we made it so, I quote from page 402 of Programming Perl, 3rd ed.

Perl should remain one language, rather than forking into a byte-oriented Perl and a character-oriented Perl.

When Programming Perl, 3rd ed. was written, not even Perl 5.6.0 had been born yet, many features documented in the book remained unimplemented for a long time. Perl 5.8 corrected much of this, and the introduction of the UTF8 flag is one of them. You can think of there being two fundamentally different kinds of strings and string-operations in Perl: one a byte-oriented mode for when the internal UTF8 flag is off, and the other a character-oriented mode for when the internal UTF8 flag is on.

Here is how Encode handles the UTF8 flag.

When you encode, the resulting UTF8 flag is always off.

When you decode, the resulting UTF8 flag is on--unless you can unambiguously represent data. Here is what we mean by "unambiguously". After $utf8 = decode("foo", $octet),

When $octet is... The UTF8 flag in $utf8 is
---------------------------------------------
In ASCII only (or EBCDIC only) OFF
In ISO-8859-1 ON
In any other Encoding ON
---------------------------------------------

As you see, there is one exception: in ASCII. That way you can assume Goal #1. And with Encode, Goal #2 is assumed but you still have to be careful in the cases mentioned in the CAVEAT paragraphs above.

This UTF8 flag is not visible in Perl scripts, exactly for the same reason you cannot (or rather, you don't have to) see whether a scalar contains a string, an integer, or a floating-point number. But you can still peek and poke these if you will. See the next section.

[INTERNAL] Turns the STRING's internal UTF8 flag on. The STRING is not checked for containing only well-formed UTF-8. Do not use this unless you know with absolute certainty that the STRING holds only well-formed UTF-8. Returns the previous state of the UTF8 flag (so please don't treat the return value as indicating success or failure), or undef if STRING is not a string.

NOTE: For security reasons, this function does not work on tainted values.

[INTERNAL] Turns the STRING's internal UTF8 flag off. Do not use frivolously. Returns the previous state of the UTF8 flag, or undef if STRING is not a string. Do not treat the return value as indicative of success or failure, because that isn't what it means: it is only the previous setting.

NOTE: For security reasons, this function does not work on tainted values.

....We now view strings not as sequences of bytes, but as sequences
of numbers in the range 0 .. 2**32-1 (or in the case of 64-bit
computers, 0 .. 2**64-1) -- Programming Perl, 3rd ed.

That has historically been Perl's notion of UTF-8, as that is how UTF-8 was first conceived by Ken Thompson when he invented it. However, thanks to later revisions to the applicable standards, official UTF-8 is now rather stricter than that. For example, its range is much narrower (0 .. 0x10_FFFF to cover only 21 bits instead of 32 or 64 bits) and some sequences are not allowed, like those used in surrogate pairs, the 31 non-character code points 0xFDD0 .. 0xFDEF, the last two code points in any plane (0xXX_FFFE and 0xXX_FFFF), all non-shortest encodings, etc.

The former default in which Perl would always use a loose interpretation of UTF-8 has now been overruled:

From: Larry Wall <larry@wall.org>
Date: December 04, 2004 11:51:58 JST
To: perl-unicode@perl.org
Subject: Re: Make Encode.pm support the real UTF-8
Message-Id: <20041204025158.GA28754@wall.org>
On Fri, Dec 03, 2004 at 10:12:12PM +0000, Tim Bunce wrote:
: I've no problem with 'utf8' being perl's unrestricted uft8 encoding,
: but "UTF-8" is the name of the standard and should give the
: corresponding behaviour.
For what it's worth, that's how I've always kept them straight in my
head.
Also for what it's worth, Perl 6 will mostly default to strict but
make it easy to switch back to lax.
Larry

Got that? As of Perl 5.8.7, "UTF-8" means UTF-8 in its current sense, which is conservative and strict and security-conscious, whereas "utf8" means UTF-8 in its former sense, which was liberal and loose and lax. Encode version 2.10 or later thus groks this subtle but critically important distinction between "UTF-8" and "utf8".

This project was originated by the late Nick Ing-Simmons and later maintained by Dan Kogai <dankogai@cpan.org>. See AUTHORS for a full list of people involved. For any questions, send mail to <perl-unicode@perl.org> so that we can all share.

While Dan Kogai retains the copyright as a maintainer, credit should go to all those involved. See AUTHORS for a list of those who submitted code to the project.